Introduction

The red flag with castle appeared after 1470, mainly white castle on a red background but the reverse also is known. In the 16th century the plain flag appeared with full arms. The whaling vessels used a flag (red or white?) with a whale. The war ships bore a on red background a destroyer with weapons, attested 1863. The Admiralty flag was created c. 1624. After 1600 the shield was missing on the flags and the castle was drawn directly on
the background. The castle was white or red and the background red or white. In the 17th century is attested a blue flag with a white castle. The red, white and blue ensigns have the same system as the British Navy and Hanoverian Navy. After 1751 the red flag with a white castle was imposed. Castle versions are known at least from 1751, 1834, 1862, 1894 and 1948.
Jaume Ollé (?), 4 Oct 1998

About hanseatic pennants

"Flüger" also "Flügel" or "Vlugher" are small pennants that were hoisted in the top of the mainmast of a vessel. I don't know the ratio of those pennants. Some may have been splitflags, some may have been trapeziums, some may have been triangular or even rectangular. The vessels of Hamburg were the first ones hoisting a "Flüger".
In the "Hamburger Schiffsrecht von 1270" (oldest naval law about flags in Germany) you can read:

The language is probably Mittelniederdeutsch which was the commercial language used e.g. for treaties by the merchants of the Hanse league in those days. The letter "u" is sometimes used instead of the letter "v".
Translation:
"Everyone of our citizens shall hoist a red pennant (=vlugher/ulugher), those who do not do so shall be punished by a fee of 3 Marks in silver for communal purposes, except they have pulled down the flag in case of danger. If a foreigner hoists a red pennant, he shall pay the same fee, when he is accused by our court."

Afterwards also other towns of the Hansa used pennants as distinguishing marks of their own vessels. The following five images are based upon the paintings of E.Paschke. The genuine source of the pennants I don't know. The years added to the single pennants are probably those years the pennants were reported. All pennants are depicted as trapeziums.
Klaus-Michael Schneider, 28 Nov 2005

Convoyers

After the decline of Hansa League the people of Hamburg became aware of the fact that the had to get in charge of military protection at sea by own efforts. In 1623 the admiralty was established.
In 17th century the trade with the peninsula suffered seriously under attacks of North African pirates. First operating offshore of Africa the pirates exceeded their operation area all over Eastern Atlantic, the Channel straight up to the German Bight. Though merchant ships were armoured, they were overpowered by pirates, who robbed the cargo and kidnapped the crews in order to sell them on African slave markets.
After having released slaves by money of a special budget, finally Hamburg decided to built up own frigates in order to accompany the Hamburg merchant vessels.
The construction of the "LEOPOLDUS PRIMUS" had been finished in 1668, of its sister "WAPEN VON HAMBURG"(no.1) (niederdtsch; engl. = weapons/arms of Hamburg) had been finished one year later. The latter was commanded by Hamburg's sea hero B. Karpfanger, who died, when his ship exploded in in the Bay of CÓdiz on 10 October 1683.
"LEOPOLDUS PRIMUS" remained in service until 1703.
Later the following ships had been built:
"WAPEN VON HAMBURG"(no.2) (1686-1718); "ADMIRALIT─T VON HAMBURG" (=admiralty of Hamburg)(1691-1728), dismantled in 1738 and finally sold in 1748, "DIE HOFFNUNG"(=hope) aka "ESPERANZA"(1697-1716), "WAPEN VON HAMBURG"(no.3) (1722-1738) and finally "WAPEN VON HAMBURG"(no.4) (1740-1777), which undertook only one voyage in 1746.
Afterwards the protection of Hamburg merchants was realized by the French fleet based on a treaty between France and Hamburg.
Peter Tamm: "Hamburgs Convoyschiffe"
published in: Jörg Duppler; editor : "Hamburg zur See - martime und militärische Beiträge zur Geschichte Hamburgs"; publ. in Herford, Bonn 1989
ISBN 3 - 8132 - 0318 - 2 p.45 - 52

About the flags below reported 1669:
The white flags and the masthead pennants taken from the paintings of SUHR seem to be doubtful. The underlines are containing some serious mistakes. Suhr dates his image 1669, when both ships had not yet been finished. Furthermore the "LEOPOLDUS PRIMUS" is denoted as "KAISER LEOPOLD" and both vessels are denoted as "last orlog ships" being indeed the first ones.
I can say nothing, whether the red flag of "LEOPOLDUS PRIMUS" in Hamburgmuseum is trustworthy.
Klaus-Michael Schneider, 14 May 2010

Znamierowski 1999 and Znamierowski 2001, (German translation), p.13 are showing several interesting flags of the Port Cities of northern Europe. These are derived from gonfanons, originally red in color. The flags, in a banner form [i.e. hanging flags], were flown from the stern of the vessels, the mast carrying the gonfanon of the colors. The oldest of the series that Znamierowski 1999 shows dates from the mid-13th century, that of Hamburg.

Phil Nelson, 20 Feb 2000

The German editors of Norie and Hobbs 1971 added two charts (which were not originally in Norie and Hobbs 1848) with German flags that were important over time. One of them is no. 30, Flüger: Hamburg 1270, as the above flag, but extended horizontally to a long flying flag. I believe a Flüger is a pennant of which the part near the hoist fixed to a piece of wood, and that is indeed how these are pictured in Norie and Hobbs 1971.
Peter Hans van der Muijzenberg, 12 Nov 2001

Source of following five images: Poster entitled: "Die geschichtliche Entwicklung der als deutsche Nationalflaggen auf See gefahrenen und von den seefahrenden Nationen anerkannten deutschen Kriegs- und Handelsflaggen",
(engl: "The historical evolution of those German national flags used on ships and recognized as German war flags or merchant flags by the naval nations",
edited by Deutsches Schifffahrtsmuseum Bremerhaven, 1981, based on an original
version of Kapitän zur See a.D. Karl Schultz, all flags on the poster are painted by E. Paschke, all the pictures are all fairly small,approximated size a little bit more than 3 cm2.The poster was still available up till 27 Dec 2003.
Klaus-Michael Schneider, 28 Nov 2005

Hamburg since 1500

2) Hamburg since 1500: A plain red pennant with a white shield shifted to the hoist, in the shield there is a red castle with an open black gate and three towers.
Klaus-Michael Schneider, 28 Nov 2005

Hamburg since 1500 variant

image by Klaus-Michael Schneider, 28 Nov 2005

3) Hamburg since 1500: The same as no. 2 (based on Paschke) with one difference: the castle has two red doorsteps, the castle is the same like that on the 1568-flag of Hamburg, which is also based on the paintings of Paschke.
Klaus-Michael Schneider, 28 Nov 2005

Flag with shield Hamburg 1568

image by Klaus-Michael Schneider, 15 Oct 2007

The German editors of Norie and Hobbs 1971 added two charts (which were not originally in Norie and Hobbs 1848) with German flags that were important over time. One of them is no. 20, Hamburg 1568: red flag, offset a silver shield with a red three-towered with black gate and windows black, standing on red ground.

Peter Hans van der Muijzenberg, 12 Nov 2001

Hamburg 1568: It is a plain red flag with a white shield shifted to the hoist. In the shield there is a red gate with an open black door and three towers, each with a single black window. The castle has two red doorsteps.
Klaus-Michael Schneider, 15 Oct 2007

Hamburg 1644

image by Klaus-Michael Schneider, 15 Oct 2007

Hamburg 1644: It is a plain red flag with a white gate on it shifted to the hoist. The gate has three towers with black windows and probably white crosses on the tops of the left and right tower, probably a white
double cross on the mid tower. In the basement there are black (open windows) and one white (closed) window. The door of the gate/ castle is open.
Klaus-Michael Schneider, 15 Oct 2007

Flags of convoy ship 'LEOPOLDUS PRIMUS' reported 1669

White flag with Greater Arms 1669

The flag shows in a white field a red castle with open gate supported by two golden(=yellow) rampant reguardant lions, standing on a basement of the same colour.

Red masthead pennant 1669

It is a red pennant with a white castle with open gate at the hoist. The ratio is approx 1:14. It is a swallow tail pennant. The ratio between unsplit and split part is appox 5:9.
Source: coloured painting of Christopher und Peter Suhr, depicted on this website

Red flag 1669

It is a red flag with a white castle with open gate in the upper hoist corner.
Source: I spotted this flag upon the stern of a model of the "LEOPOLDUS PRIMUS" in Hamburgmuseum on 9 August 2008.
Klaus-Michael Schneider, 14 May 2010

Flags of convoy ship 'WAPEN VON HAMBURG' (no.I) reported 1669

White flag 1669

The flag shows in a white field a red castle with open gate.

White masthead pennant 1669

It is a white pennant with a a red castle with open gate at the hoist. The ratio is approx 1:14. It is a swallow tail pennant. The ratio between unsplit and split part is appox 5:9.
Source: coloured painting of Christopher und Peter Suhr, depicted on this websiteKlaus-Michael Schneider, 14 May 2010